dengue 3y1 2
TRANSCRIPT
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ArbovirusesThe Arboviruses are also called as Arthropod borne viruses,represent an ecological grounding of viruses with complextransmission cycles involving Arthropods
These viruses have diverse physical and chemical propertiesand are classified in several virus families.
Dengue infection is caused by Arboviruses
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History DengueThis disease was first described 1780, and the virus was
isolated by Sabin 1944. Dengue virus infection is the mostcommon arthropod-borne disease worldwide with an
increasing incidence in the tropical regions of Asia, Africa,and Central and South America. There are four serotypes ofthe virus. All are transmitted by mosquitoes, which are notaffected by the disease, although an infected mosquito may
infect others (not via man).
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CurrentTrends In the 1980s, DHF began a second expansion into Asia
when Sri Lanka, India, and the Maldives Islands had theirfirst major DHF epidemics; Pakistan first reported an
epidemic of dengue fever in 1994. The epidemics in SriLanka and India were associated with multiple dengue virusserotypes, but DEN-3 was predominant and was geneticallydistinct from DEN-3 viruses previously isolated from
infected persons in those countries.
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Prevalence of Dengue Infection
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Dengue Infection and
Implications Dengue virus (DENV) infects 50 million (WHO) to 100
million (NIH) people annually. Forty percent of the worlds
population, predominately in the tropics and sub-tropics, isat risk for contracting dengue virus. DENV infection cancause dengue fever, dengue hemorrhagic fever, dengueshock syndrome, and death.
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Dengue
Mosquito transmitted Viral Infection
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What causes Dengue
Dengue (DF) and dengue hemorrhagic fever (DHF) arecaused by one of four closely related, but antigenicallydistinct, virus serotypes (DEN-1, DEN-2, DEN-3, andDEN-4), of the genus Flavivirus. Infection with one of theseserotypes provides immunity to only that serotype for life,
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Aedes aegypti
Vector
Aedes aegypti, a domestic, day-biting mosquito thatprefers to feed on humans, is the most commonAedesspecies. Infections produce a spectrum of clinicalillness ranging from a nonspecific viral syndrome tosevere and fatal hemorrhagic disease. Other species ofAedes can also transmit.
http://www.cdc.gov/ncidod/dvbid/dengue/ae-aegypti-feeding.htmhttp://www.cdc.gov/ncidod/dvbid/dengue/ae-aegypti-feeding.htmhttp://www.cdc.gov/ncidod/dvbid/dengue/ae-aegypti-feeding.htmhttp://www.cdc.gov/ncidod/dvbid/dengue/ae-aegypti-feeding.htm -
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Dengue VirusA Flavivirius Flavivirius are spherical and
40- 60 mm in diameter.
GenomePositive sense,single sense RNA,11kb in size
GenomeRNA infectious
Enveloped virus
Three structural polypeptides
two are glycosylatedReplication in cytoplasam
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How Mosquitos spread the infectionThe disease starts during the rainy season, when vector
Mosquito Aedes aegypti is abundant
The Aedes breeds in the tropical or semitropicalclimates in water holding receptacles or in plants closeto human dwellings
A female Aedes acquires the infection feeding upon aviremic human.After a period of 814 days mosquitoes are infective
and remain infective for life. ( 1- 3 ) months.
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Dengue - Endemics Persons living in a dengue-endemic area can have more
than one dengue infection during their lifetime. DF andDHF are primarily diseases of tropical and sub tropicalareas, and the four different dengue serotypes aremaintained in a cycle that involves humans and the Aedesmosquito.
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Clinical Manifestations
Any or few of the following events can occur.
Fever,
Severe head ache Muscle and joint pains
Nausea, vomiting,
Eye pain
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How Dengue Infection starts and manifests
Incubation period 47 days ( 314 days) Fever may start with, Malise,chills,head ache Soon leads to severe back ache, joint pains, muscular pain, pain in
the eye ball. Temperature may persist for 3 -5 days. On some occasions once again raises in about 58 days ( Saddle
back fever ) Myalgia may be severe with deep bone pain
( Break bone fever ) characteristic of the Disease
On majority of the occasions a self limited condition,Subside on its own
Death is a rare event.
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Dengue with Rashes
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Dengue Hemorrhagic Fever Common in children.
In children passively acquired contributed by the maternalantibodies transferred to the fetus.
In other ( Adults ) the presence of antibodies due toprevious infection with different serotype
Initially presents like classical Dengue infection
But patients condition abruptly worsens, an important causeof morbidity and mortality in Dengue
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Risk factor for DHF Important risk factors for DHF include the strain of the
infecting virus, as well as the age, and especially the priordengue infection history of the patient
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Dengue Hemorrhagic Syndrome Chateresied by shock and hemoconcentration
Contributed by circustantial evidence suggests secondary
infection with Dengue type 2 following type 1 infection inthe past.
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Pathogenesis Presence of existing Dengue antibody, associated with fresh
viral infection with new serotype complexes and formswithin few days of the second dengue infection.
Non neutralizing enhancing antibodies promote infection ofhigher number of Mononuclear cells.
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Dengue Hemorraghigic Syndrome DHS is caused due to release of,
1 Release of cytokines
2 Vasoactive mediators.3 Procoagulants
Manifest with disseminated
intravascular coagulation
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Risk of Hemorrhagic FeverThe risk of hemorrhagic fever syndrome is about 0.2%
during the first attack
The second attack with different serotype increases therisk to ten fold
The fatality rate with dengue hemorrhagic fever canreach 15% but proper medical care and symptomaticmangement can reduce mortality to less than 1%
On few occasions patients condition abruptly worsensinto Dengue shock syndrome, a more severe form ofdisease characterized by shock and hemoconcentration.
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DiagnosisIn resource rich establishments
1 Reverse transcriptase polymerase chain reaction methods
help rapid identification2 Isolation of virus is difficult
3 The current favored approach is inoculation of mosquitocell line with patient serum coupled with nucleic acid assay
to identify a recovered virus.
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Dengue SerologyThe serology is limited with cross reactivity of IgG
antibodies to heterologus Flavivirius antigens
Most commonly used methods areViral protein specific capture IgM or IgG by ELISA
IgM antibodies develop within few days of illness
Neutralizing anti Hemagglutination inhibiting antibodiesappear within a week after onset of Dengue fever
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Importance of paired sample testing in
Serology
Testing one sample for serum and reporting a negative testis fallacious
Analysis of paired acute andconvalescent sera to show significant
rise in antibody titer is the most reliableevidence of an active dengue infection.
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Newer Diagnostic MethodsRT - PCR
RT PCR is a highlysensitive tool in
Diagnosis, withestablished highsensitivity in Diagnosisin Puzzles
Developing world lacksresources toimplement and utilizethe Scientific advances
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Immunology in Dengue Four serotypes exist distinguished by Molecular basis and Nt
tests
Infection confers life long immunity
But cross protection between serotypes is of short duration.
Reinfection with different serotype after primary attack ismore dangerous causes Dengue hemorrhagic fever.
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Dengue a Reemerging Infection Dengue in 2005 identified as the most important mosquito
borne viral disease
An estimated 50 million or more cases occur annuallyworldwide
400,000 cases of dengue hemorrhagic fever.
Asian counties report major cases of childhood deaths
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Treatment No Anti viral therapy available
Symptomatic management in Majority of cases
Dengue Hemorrhagic fever to be treated with suitable fluidreplacement
No Vaccine available, difficult in view of four serotypes.
PREVENT MULTIPLICATION OF
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PREVENT MULTIPLICATION OF
MOSQUITOES
Mosquitoes which spread dengue live and breed in and aroundhouses.
Drain water from coolers, tanks, barrels, drums and buckets, etc.;
There should be no water in coolers when not in use;
Remove from the house all objects, e.g. plant saucers, etc. whichhave water collected in them;
Remove water from refrigerator drip pans every other day;
All stored water containers should be kept covered all the time;
Discard solid waste and objects where water collects, e.g. bottles,tins, tyres, etc.
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PREVENT MOSQUITO BITES
Dengue mosquitoes bite during the daytime. Protect yourself
from the bite. Wear full sleeve clothes and long dresses to cover the limbs;
Repellentcare should be taken in using repellents on smallchildren and the elderly;
Use mosquito coils and electric vapour mats during the daytimeto prevent Dengue;
Use mosquito netsto protect babies, old people and others,who may rest during the day. The effectiveness of such nets can
be improved by treating them with permethrin (pyrethroidinsecticide). Curtains (cloth or bamboo) can also be treated withinsecticide and hung at windows or doorways, to repel or killmosquitoes.
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Epidemiology - Dengue Dengue virus are distributed world wide in tropical regions.
Where the Aedes vectors exist, are endemic areas
Changing and increasing incidences are associated with rapidurban population growth, over crowding and lax mosquitocontrol measures
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Febrile Phase
In the early febrile phase, it is not possible to distinguish DFfrom DHF.
Their treatments during the febrile phase are the same, i.e.symptomatic and supportive:
Rest. Do not give Aspirin or Brufen. Aspirin can cause gastritis and/or
bleeding. In children, Reyes syndrome (encephalopathy) may be aserious complication. Do not give antibiotics as these do not help. Oral rehydration therapy2 is recommended for patients with
moderate dehydration caused by vomiting and high temperature.
Food should be given according to appetite. Paracetamol (not more than 4 times in 24 hours) according:Age
Dose(tablet 250 mg)
Mg/Dose
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Afebrile Phase
Dengue Fever
Constitutional symptoms in patients with DF after the fallof fever are as during the febrile stage. Most patients willrecover without complication. Treatment should be carriedout as indicated
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Afebrile Phase
Dengue Haemorrhagic Fever (DHF) Grades I and II
As in DF, during the afebrile phase of DHF Grades I and II, thepatient has the same symptoms as during the febrile phase. The clinicalsigns plus thrombocytopenia and hemoconcentration or rise inhematocrit are sufficient to establish a clinical diagnosis of DHF.During this phase, the patients should be observed for at least 2-3 days
after the fall in temperature, for rashes on the skin, bleeding from noseor gums, blue spots on the skin or tarry stools. If any of these signs areobserved, the patients should be brought to the hospital without delay.
The only difference between the DF and DHF Grade I is the presenceof thrombocytopenia and rise in hematocrit (>20%). Patients withDHF Grade I do not usually require intravenous fluid therapy and
ORT is sufficient. Intravenous fluid therapy may need to beadministered only when the patient is vomiting persistently or severely,or refusing to accept oral fluids. Patients with DHF Grade Iwho live faraway from the hospital or those who are not likely to beable to followthe medical advice should be kept in the hospital for observation .
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What not to do
Do not give Aspirin or Brufen for treatment of fever.Avoid giving intravenous therapy before there is evidence of
hemorrhage and bleeding.Avoid giving blood transfusion unless indicated, reduction
in hematocrit or severe bleeding.Avoid giving steroids. They do not show any benefit. Do not use antibiotics Do not changes the speed of fluid rapidly, i.e. avoid rapidly
increasing or rapidly slowing the speed of fluids.
Insertion of nasogastric tube to determine concealedbleeding or to stop bleeding (by cold lavage) is notrecommended since it is hazardous.
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Signs of Recovery
Stable pulse, blood pressure and breathing rate
Normal temperature
No evidence of external or internal bleeding Return of appetite
No vomiting
Good urinary output
Stable haematocrit
Convalescent confluent petechiae rash
Avoiding Mosquito bites
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Avoiding Mosquito bites
remain only way to prevent
DENGUE